The present invention relates to a polishing apparatus for polishing an article such as a semiconductor wafer, and in particular, relates to a polishing apparatus provided with an attitude controller for controlling an attitude of a turntable which is provided with a polishing surface and/or a carrier for carrying an article to be polished and bringing it into contact with the polishing surface of the turntable.
With recent rapid progress in technology for fabricating high-integration semiconductor devices, circuit wiring patterns have been becoming increasingly fine, with spaces between wiring patterns also decreasing. As wiring spacing decreases to less than 0.5 microns, the depth of focus in circuit pattern formation in photolithography and the like becomes shallower. Accordingly, surfaces of semiconductor wafers on which circuit pattern images are to be formed by a stepper are required to be polished by a polishing apparatus to an exceptionally high degree of surface flatness or planarization. As one method for effecting such planarization, for example, a chemical/mechanical polisher (CMP) has recently been used, in which polishing is carried out while a polishing solution having a predetermined chemical composition is supplied.
FIG. 26 shows such a conventional polisher for polishing a semiconductor wafer. The polisher includes a turntable 52 provided on its upper surface with a polishing cloth 51 and a wafer carrier 54 for holding a semiconductor wafer 53. In a polishing operation, the turntable and the wafer carrier are independently rotated about their axes by motors (not shown) while the wafer 53 is engaged with the polishing cloth 51 and an abrasive liquid Q is supplied through a nozzle 57 provided above the turntable. However, during polishing, if the polishing cloth 51 does not engage with the wafer 53 under a uniform pressure across respective engaging surfaces, the wafer fails to be polished evenly. To solve this problem, the conventional polishing apparatus is provided with a universal joint comprising a ball bearing 56 between the wafer carrier 54 and a drive shaft 55 for pressing the wafer 53 against the polishing cloth 51 while drivingly rotating the wafer carrier 54. The universal joint enables the wafer 54 to tilt about the ball bearing 56 in response to inclinations in the polishing surface of the polishing cloth 51. Consequently, the polishing surface of the polishing cloth 51 and the polished surface of the wafer 53 held by the wafer carrier 54 are kept in a parallel relation with each other, whereby pressure between the wafer and the polishing cloth is kept even across the entire surface of the water. Japanese Patent Application 06198561 A discloses such a universal joint.
However, as stated above, since the drive shaft presses the wafer 53 against the polishing cloth 51 under a pressure F, a friction force xcexcF, in which xcexc is a friction coefficient, is generated and this causes a rotational moment M=xcexcFH, in which H is a height of the center of the ball bearing 56 relative to the upper surface of the polishing cloth 51. The wafer 53 is thus inclined downward in a direction opposite to the direction D in which the polishing cloth 51 on the turntable 52 passes under the wafer 53, with the result that the wafer 53 is subject to an uneven pressure imposed by the polishing cloth 51. To make the rotational moment M zero, it is necessary to make the above-noted height H zero. There is proposed an apparatus in which the center of tilting is positioned at a level of engagement between a wafer and a polishing cloth.
In theory, if the center of tilting lies on a surface where the polishing cloth and the wafer engage with each other, the rotational moment M which tends to tilt the wafer carrier will become zero and thus the wafer carrier can be kept parallel to the turntable. However, in practice, the polishing surface or upper surface of the polishing cloth on the turntable is not exactly even across its entire area which gives rise to a change in inclination of the polishing surface which is in contact with the wafer when the turntable is rotated. As a consequence of such a change in inclination of the polishing surface, the wafer carrier tends to tilt excessively under its inertia moment resulting in unstable tilting. Consequently, the wafer is unable to be engaged with the polishing cloth under a uniform pressure.
JP 1058308A discloses a polishing apparatus which is provided with an electromagnetic bearing including an electromagnetic thrust bearing device and an electromagnetic radial bearing device for bearing a drive shaft of a wafer carrier with an electromagnetic force, and an attitude controller for controlling the attitude of the drive shaft to keep the wafer carrier parallel to a turntable.
However, since in the polishing apparatus in accordance with JP 1058308A, the drive shaft of the wafer carrier is designed to be supported only by the electromagnetic bearing under the influence of the electromagnetic force generated thereby, it involves the following problems:
1) It is necessary for the thrust bearing device to be capable of generating a large magnetic force to press a wafer against the polishing cloth.
2) In terms of design, a motor for actuating the wafer carrier is required to be accommodated in a housing which also houses the electromagnetic bearing, and thus the size of the housing becomes large.
3) The wafer carrier is required to be movable up and down so as to load and unload a semiconductor wafer. This means that the wafer carrier, the electromagnetic bearing and the motor noted above are required to be moved as a unit and thus a mechanism for moving the unit also becomes large.
The present invention aims to solve the problems 1)-3) outlined above and, specifically, to provide a polishing apparatus which includes an attitude controller for controlling an attitude of a wafer carrier and/or a turntable so that the wafer or an object to be polished can be engaged with a polishing cloth on a turntable with a uniform pressure being exerted across its entire area.
In view of the above-described circumstances, an object of the present invention is to provide a polishing apparatus with an attitude controller for controlling an attitude of a turntable and/or a carrier for carrying an article to be polished, whereby the article is engaged with a polishing surface on the turntable under a uniform pressure thereby being polished to a very high degree of flatness.
In accordance with one aspect of this invention, there is provided a polishing apparatus comprising a turntable having a polishing surface that comes into sliding contact with an object to be polished, a support for tiltably supporting the turntable, and, an attitude controller for controlling an attitude or orientation of the turntable. The attitude controller may control the attitude of the turntable by controlling an angle of tilting of the turntable relative to the support by virtue of an electromagnetic force. The polishing apparatus may include a stationary frame, and the attitude controller may comprise an electromagnetic device fixedly provided on the stationary frame of the polishing apparatus, and an armature fixedly provided on the turntable and adapted to be moved by virtue of an electromagnetic force generated by the electromagnetic device. The attitude controller may comprise a cylinder device provided under the turntable and fixed to a stationary frame of the polishing apparatus and engaged with a lower surface of the turntable so that the cylinder device controls the attitude of the turntable by extension and retraction thereof.
In accordance with another aspect of the present invention, there is provided a polishing apparatus comprising a turntable having a polishing surface, a carrier for holding an article to be polished in a sliding contact relation with the polishing surface, a pressing device connected to the carrier and adapted to press the carrier towards the turntable with the article engaged with the polishing surface, and an attitude controller for controlling an attitude or orientation of the carrier. The pressing device may be a drive shaft for drivingly rotating the wafer carrier and the polishing apparatus includes a universal joint connecting the drive shaft and the carrier in such a manner that the carrier can tilt relative to the drive shaft. The attitude controller may comprise an electromagnetic device fixedly provided on a frame for rotatably supporting the drive shaft and an armature fixedly provided on the carrier and adapted to be moved by virtue of an electromagnetic force generated by the electromagnetic device. The attitude controller includes a sensor for sensing the attitude or orientation of the carrier so that the attitude controller controls the attitude of the wafer in response to the sensed attitude or orientation. The polishing apparatus may further include a pressing member provided radially outside the carrier and movable up and down independently of the carrier, an urging device for urging the pressing member, and a bearing for supporting the pressing member on the carrier in such a manner that the pressing member is kept stationary while allowing the carrier to rotate. The carrier may include a mounting member connected to the pressing device and an article holding member with a gap interposed therebetween, and the article holding member has a lower surface for holding an article to be polished and is flexible so that it can be deformed in both a concave and convex manner in a vertical direction by controlling a pressure in the gap. The carrier may include a retainer ring provided on the outer periphery of the carrier to confine the article held on the lower surface of the holding member. The retainer ring is movable vertically relative to the holding member, and the carrier further includes a pressing device for pressing the retainer ring vertically against the polishing surface of the turntable.
In accordance with yet another aspect of this invention, there is provided a polishing apparatus including both the turntable attitude controller and the carrier attitude controller as noted above.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.